linux/fs/squashfs/block.c

// SPDX-License-Identifier: GPL-2.0-or-later
/*
 * Squashfs - a compressed read only filesystem for Linux
 *
 * Copyright (c) 2002, 2003, 2004, 2005, 2006, 2007, 2008
 * Phillip Lougher <phillip@squashfs.org.uk>
 *
 * block.c
 */

/*
 * This file implements the low-level routines to read and decompress
 * datablocks and metadata blocks.
 */

#include <linux/blkdev.h>
#include <linux/fs.h>
#include <linux/vfs.h>
#include <linux/slab.h>
#include <linux/pagemap.h>
#include <linux/string.h>
#include <linux/bio.h>

#include "squashfs_fs.h"
#include "squashfs_fs_sb.h"
#include "squashfs.h"
#include "decompressor.h"
#include "page_actor.h"

/*
 * Returns the amount of bytes copied to the page actor.
 */
static int copy_bio_to_actor(struct bio *bio,
			     struct squashfs_page_actor *actor,
			     int offset, int req_length)
{
	void *actor_addr;
	struct bvec_iter_all iter_all = {};
	struct bio_vec *bvec = bvec_init_iter_all(&iter_all);
	int copied_bytes = 0;
	int actor_offset = 0;

	squashfs_actor_nobuff(actor);
	actor_addr = squashfs_first_page(actor);

	if (WARN_ON_ONCE(!bio_next_segment(bio, &iter_all)))
		return 0;

	while (copied_bytes < req_length) {
		int bytes_to_copy = min_t(int, bvec->bv_len - offset,
					  PAGE_SIZE - actor_offset);

		bytes_to_copy = min_t(int, bytes_to_copy,
				      req_length - copied_bytes);
		if (!IS_ERR(actor_addr))
			memcpy(actor_addr + actor_offset, bvec_virt(bvec) +
					offset, bytes_to_copy);

		actor_offset += bytes_to_copy;
		copied_bytes += bytes_to_copy;
		offset += bytes_to_copy;

		if (actor_offset >= PAGE_SIZE) {
			actor_addr = squashfs_next_page(actor);
			if (!actor_addr)
				break;
			actor_offset = 0;
		}
		if (offset >= bvec->bv_len) {
			if (!bio_next_segment(bio, &iter_all))
				break;
			offset = 0;
		}
	}
	squashfs_finish_page(actor);
	return copied_bytes;
}

static int squashfs_bio_read_cached(struct bio *fullbio,
		struct address_space *cache_mapping, u64 index, int length,
		u64 read_start, u64 read_end, int page_count)
{
	struct page *head_to_cache = NULL, *tail_to_cache = NULL;
	struct block_device *bdev = fullbio->bi_bdev;
	int start_idx = 0, end_idx = 0;
	struct bvec_iter_all iter_all;
	struct bio *bio = NULL;
	struct bio_vec *bv;
	int idx = 0;
	int err = 0;

	bio_for_each_segment_all(bv, fullbio, iter_all) {
		struct page *page = bv->bv_page;

		if (page->mapping == cache_mapping) {
			idx++;
			continue;
		}

		/*
		 * We only use this when the device block size is the same as
		 * the page size, so read_start and read_end cover full pages.
		 *
		 * Compare these to the original required index and length to
		 * only cache pages which were requested partially, since these
		 * are the ones which are likely to be needed when reading
		 * adjacent blocks.
		 */
		if (idx == 0 && index != read_start)
			head_to_cache = page;
		else if (idx == page_count - 1 && index + length != read_end)
			tail_to_cache = page;

		if (!bio || idx != end_idx) {
			struct bio *new = bio_alloc_clone(bdev, fullbio,
							  GFP_NOIO, &fs_bio_set);

			if (bio) {
				bio_trim(bio, start_idx * PAGE_SECTORS,
					 (end_idx - start_idx) * PAGE_SECTORS);
				bio_chain(bio, new);
				submit_bio(bio);
			}

			bio = new;
			start_idx = idx;
		}

		idx++;
		end_idx = idx;
	}

	if (bio) {
		bio_trim(bio, start_idx * PAGE_SECTORS,
			 (end_idx - start_idx) * PAGE_SECTORS);
		err = submit_bio_wait(bio);
		bio_put(bio);
	}

	if (err)
		return err;

	if (head_to_cache) {
		int ret = add_to_page_cache_lru(head_to_cache, cache_mapping,
						read_start >> PAGE_SHIFT,
						GFP_NOIO);

		if (!ret) {
			SetPageUptodate(head_to_cache);
			unlock_page(head_to_cache);
		}

	}

	if (tail_to_cache) {
		int ret = add_to_page_cache_lru(tail_to_cache, cache_mapping,
						(read_end >> PAGE_SHIFT) - 1,
						GFP_NOIO);

		if (!ret) {
			SetPageUptodate(tail_to_cache);
			unlock_page(tail_to_cache);
		}
	}

	return 0;
}

static struct page *squashfs_get_cache_page(struct address_space *mapping,
					    pgoff_t index)
{
	struct page *page;

	if (!mapping)
		return NULL;

	page = find_get_page(mapping, index);
	if (!page)
		return NULL;

	if (!PageUptodate(page)) {
		put_page(page);
		return NULL;
	}

	return page;
}

static int squashfs_bio_read(struct super_block *sb, u64 index, int length,
			     struct bio **biop, int *block_offset)
{
	struct squashfs_sb_info *msblk = sb->s_fs_info;
	struct address_space *cache_mapping = msblk->cache_mapping;
	const u64 read_start = round_down(index, msblk->devblksize);
	const sector_t block = read_start >> msblk->devblksize_log2;
	const u64 read_end = round_up(index + length, msblk->devblksize);
	const sector_t block_end = read_end >> msblk->devblksize_log2;
	int offset = read_start - round_down(index, PAGE_SIZE);
	int total_len = (block_end - block) << msblk->devblksize_log2;
	const int page_count = DIV_ROUND_UP(total_len + offset, PAGE_SIZE);
	int error, i;
	struct bio *bio;

	bio = bio_kmalloc(page_count, GFP_NOIO);
	if (!bio)
		return -ENOMEM;
	bio_init(bio, sb->s_bdev, bio->bi_inline_vecs, page_count, REQ_OP_READ);
	bio->bi_iter.bi_sector = block * (msblk->devblksize >> SECTOR_SHIFT);

	for (i = 0; i < page_count; ++i) {
		unsigned int len =
			min_t(unsigned int, PAGE_SIZE - offset, total_len);
		pgoff_t index = (read_start >> PAGE_SHIFT) + i;
		struct page *page;

		page = squashfs_get_cache_page(cache_mapping, index);
		if (!page)
			page = alloc_page(GFP_NOIO);

		if (!page) {
			error = -ENOMEM;
			goto out_free_bio;
		}

		/*
		 * Use the __ version to avoid merging since we need each page
		 * to be separate when we check for and avoid cached pages.
		 */
		__bio_add_page(bio, page, len, offset);
		offset = 0;
		total_len -= len;
	}

	if (cache_mapping)
		error = squashfs_bio_read_cached(bio, cache_mapping, index,
						 length, read_start, read_end,
						 page_count);
	else
		error = submit_bio_wait(bio);
	if (error)
		goto out_free_bio;

	*biop = bio;
	*block_offset = index & ((1 << msblk->devblksize_log2) - 1);
	return 0;

out_free_bio:
	bio_free_pages(bio);
	bio_uninit(bio);
	kfree(bio);
	return error;
}

/*
 * Read and decompress a metadata block or datablock.  Length is non-zero
 * if a datablock is being read (the size is stored elsewhere in the
 * filesystem), otherwise the length is obtained from the first two bytes of
 * the metadata block.  A bit in the length field indicates if the block
 * is stored uncompressed in the filesystem (usually because compression
 * generated a larger block - this does occasionally happen with compression
 * algorithms).
 */
int squashfs_read_data(struct super_block *sb, u64 index, int length,
		       u64 *next_index, struct squashfs_page_actor *output)
{
	struct squashfs_sb_info *msblk = sb->s_fs_info;
	struct bio *bio = NULL;
	int compressed;
	int res;
	int offset;

	if (length) {
		/*
		 * Datablock.
		 */
		compressed = SQUASHFS_COMPRESSED_BLOCK(length);
		length = SQUASHFS_COMPRESSED_SIZE_BLOCK(length);
		TRACE("Block @ 0x%llx, %scompressed size %d, src size %d\n",
			index, compressed ? "" : "un", length, output->length);
	} else {
		/*
		 * Metadata block.
		 */
		const u8 *data;
		struct bvec_iter_all iter_all = {};
		struct bio_vec *bvec = bvec_init_iter_all(&iter_all);

		if (index + 2 > msblk->bytes_used) {
			res = -EIO;
			goto out;
		}
		res = squashfs_bio_read(sb, index, 2, &bio, &offset);
		if (res)
			goto out;

		if (WARN_ON_ONCE(!bio_next_segment(bio, &iter_all))) {
			res = -EIO;
			goto out_free_bio;
		}
		/* Extract the length of the metadata block */
		data = bvec_virt(bvec);
		length = data[offset];
		if (offset < bvec->bv_len - 1) {
			length |= data[offset + 1] << 8;
		} else {
			if (WARN_ON_ONCE(!bio_next_segment(bio, &iter_all))) {
				res = -EIO;
				goto out_free_bio;
			}
			data = bvec_virt(bvec);
			length |= data[0] << 8;
		}
		bio_free_pages(bio);
		bio_uninit(bio);
		kfree(bio);

		compressed = SQUASHFS_COMPRESSED(length);
		length = SQUASHFS_COMPRESSED_SIZE(length);
		index += 2;

		TRACE("Block @ 0x%llx, %scompressed size %d\n", index - 2,
		      compressed ? "" : "un", length);
	}
	if (length < 0 || length > output->length ||
			(index + length) > msblk->bytes_used) {
		res = -EIO;
		goto out;
	}

	if (next_index)
		*next_index = index + length;

	res = squashfs_bio_read(sb, index, length, &bio, &offset);
	if (res)
		goto out;

	if (compressed) {
		if (!msblk->stream) {
			res = -EIO;
			goto out_free_bio;
		}
		res = msblk->thread_ops->decompress(msblk, bio, offset, length, output);
	} else {
		res = copy_bio_to_actor(bio, output, offset, length);
	}

out_free_bio:
	bio_free_pages(bio);
	bio_uninit(bio);
	kfree(bio);
out:
	if (res < 0) {
		ERROR("Failed to read block 0x%llx: %d\n", index, res);
		if (msblk->panic_on_errors)
			panic("squashfs read failed");
	}

	return res;
}